The present invention relates to the synchronization of two devices with a data transmission method.
In the transmission of compressed data, for instance audio-visual data, textual data, video data or control information, errors in the transmission can disrupt a subsequent decompression such that the data can no longer be reconstructed correctly.
In the context of the transmission of highly compressed data currents, the following communication system architecture is known, which is illustrated in FIG. 2 (cf. [1]):
Applications of a predeterminable number of application layers Ai (i=1 . . . n) generate data Di, which are to be transmitted from a first device V1 to a second device V2.
The data Di that are to be transmitted are respectively delivered to what is known as an adaptation layer Ali, which is allocated to the respective application Ai.
The different types of adaptation layers described in [1] serve for processing different characteristic data.
Data should be understood here as, for instance, audio data, video data, textual data (in particular, data that are coded according to ASCII code)xe2x80x94generally any kind of data that can be transmitted in digital form.
From the respective adaptation layer Ali, adapted data Adi are fed to a multiplexer MUX/DEMUX for purposes of forming a combined, i.e. multiplexed, data current XD.
Via a transmission unit UE, for instance a wirebound network or a mobile radio network, the data current XD is transmitted to the second device V2. The second device V2 has the same structure as the first device V1. In the second device V2 the multiplexed data current XD is split into the individual adaptive data adi again; that is, demultiplexed. The adapted data Adi is fed by the multiplexer/demultiplexer MUX/DEMUX to the elements of the adaptation layer Ali of the second device V2. The double arrows in the individual communication paths indicate that the communication between the first device V1 and the second device V2 can occur bidirectionally.
In the method taught in ITU-T Recommendation H.223, Multiplexing Protocol for Low-Bitrate Multimedia Communication 1996, a separate error detection method and/or error correction method is carried out for the data in the adaptation layer.
The more higher-level or robust the error detection method, or the error correction method, (i.e. the more errors can be detected, or corrected in the transmission), the greater the demand for bandwidth in the transmission of the data currents grows, due to additional redundancy information that is required for error correction, or error detection. Furthermore, the complexity of the error detection, or error correction method, grows with rising executions which leads to an elevated demand for computing time both for the encoding at the sender and for the decoding at the receiver.
For this reason, documents ITU-T Recommendation H.223, Multiplexing Protocol for Low-Bitrate Multimedia Communication 1996 (cf. Reference 1); ITU-T Draft Recommendation H.223/Annex A, Multiplexing Protocol for Low-Bitrate Mobile Multimedia Communication, Level 1, Draft version, July, 1997 (cf. Reference 2); ITU-T Draft Recommendation H.223/Annex B, Multiplexing Protocol for Low-Bitrate Mobile Multimedia Communication, Level 2, Draft version, July, 1997 (cf. Reference 3); and ITU-T Draft Recommendation H.223/Annex C, Multiplexing Protocol for Low-Bitrate Mobile Multimedia Communication, Level 3, Draft version, July, 1997 (cf. Reference 4) teach the provision of various error detection methods, or respectively, error correction methods, that are more or less robust, depending on requirements, but are less or more complex, accordingly.
Reference 1, Reference 2, Reference 3, Reference 3 and Reference 4 define various methods of different levels henceforth referred to as data transmission methods (level 0 . . . 3). A first data transmission method (level 0) (corresponding to Reference 1), which every device must have implemented; a second data transmission method (level 1)(corresponding to Reference 2); a third data transmission method (level 2); and a fourth data transmission method (level 3). The error robustness, that is, the level of the method with respect to error protection (error detection, or error correction), rises from the first transmission method (level 0) to the fourth transmission method.
Every device that functions according to the method taught in ITU-T Recommendation H.223, Multiplexing Protocol for Low-Bitrate Multimedia Communication 1996 therefor; must be able to guarantee at least the first data transmission method (level 0). The additional data transmission (level 0 . . . 3)methods are optional, which means that different devices can communicate with one another that do not have the same maximal capability of error protection implemented. Problems can arise in this case, since at the beginning of the communication connection it must first be worked out according to which data transmission method the data transmission is to occur (synchronization with a data transmission method).
It is an object of the present invention to provide a method and a communication system for synchronizing two devices with a predeterminable data transmission method from a set of data transmission methods, whereby the synchronization can be accomplished simply and automatically.
This object is achieved in accordance with the present invention in a method for synchronizing two devices with a predeterminable data transmission method from a set of data transmission methods that differ with respect to their error protection for transmitted data, said method comprising the steps of: a first device and a second device respectively exchanging a first synchronization message and a second synchronization message, said first synchronization message having an item of information identifying a data transmission method having a highest-level error protection that can be executed by said first device, said second synchronization message having an item of information identifying a data transmission method having a highest-level error protection that can be executed by said second device; determining said data transmission method of said received first synchronization message at said second device from said received first synchronization message; determining said data transmission method of said received second synchronization message at said first device from said received second synchronization message; forming an additional synchronization message at one of said first and second devices by which said respectively determined data transmission method can be executed, said additional synchronization message identifying said data transmission method that can be executed by both said first device and said second device; sending said additional synchronization message to an other of said first and second devices; determining said data transmission method of said additional synchronization message at said other of said first and second devices from said additional synchronization method; and synchronizing said first device and said second device with said determined data transmission method. This object is also achieved in accordance with the present invention in a communication system for synchronizing two devices with a predeterminable data transmission method from a set of data transmission methods that differ with respect to their error protection for data to be transmitted, said communication system comprising:
a first device; and
a second device connected to said first device,
said first device and said second device respectively for exchanging a first synchronization message and a second synchronization message, said first synchronization message having an item of information identifying a data transmission method having a highest-level error protection that can be executed by said first device, said second synchronization message having an item of information identifying a data transmission method having a highest-level error protection that can be executed by said second device,
said second device for determining said data transmission method of said received first synchronization message from said received first synchronization message,
said first device for determining said data transmission method of said received second synchronization message from said received second synchronization message,
said first and second device for forming an additional synchronization message at one of said first and second devices by which said respectively determined data transmission method can be executed, said additional synchronization message identifying said data transmission method that can be executed by both said first device and said second device;
said first and second devices for sending said additional synchronization message to an other of said first and second devices;
said first and second devices for determining said data transmission method of said additional synchronization message at said other of said first and second devices from said additional synchronization method, and
said first and second devices for synchronizing said first device and said second device with said determined data transmission method.
A first device and a second device exchange synchronization messages, whereby a respective synchronization message contains an item of information identifying the data transmission method with the highest-level error protection that the respective device that has sent the synchronization message is capable of executing. The data transmission method of the respective synchronization message is ascertained by the respective receiving device from the received synchronization message. A further synchronization message is formed by the device by which the respectively determined data transmission method can be executed and is delivered to the respective other device, whereby the additional synchronization message identifies the data transmission method which both devices are capable of executing. The data transmission method of the additional synchronization message is determined from the additional synchronization message. Now the devices are synchronized with the determined data transmission method.
In an embodiment the communication system comprises a first device and a second device, which are so arranged that
a first device and a second device exchange synchronization messages, whereby a respective synchronization message contains an item of information identifying a data transmission method with the highest level of error protection that the respective device that has sent the synchronization message is capable of executing;
from the received synchronization message, the data transmission method of the respective synchronization message is respectively determined by the respective receiving device;
a further synchronization message is formed by the device by which the respectively determined data transmission method can be executed and is delivered to the respective other device, whereby the additional synchronization message identifies the data transmission method that both devices are capable of executing;
from the additional synchronization message, the data transmission method of the additional synchronization message is determined;
the devices are synchronized with the determined data transmission method.
A synchronization possibility is thus put forward with which the synchronization of two devices with respect to the data transmission method used is accomplished, and a common basis for further communication thereby established, without added complexity.
A further advantage of the invention is that it can be expanded without further ado into future data transmission methods which are not yet defined in their respective realization. The invention thus automatically always guarantees a downward-compatibility with the xe2x80x9colder devicesxe2x80x9d even given future development of the data transmission method.
The invention can clearly be seen as the exchanging by the devices of synchronization messages indicating which data transmission method is maximally supported by the respective device. Based on the type of synchronization message, the receiving device detects the data transmission method indicated and, when its own suggested data transmission method is higher-level than the one suggested by the other device, the data transmission method of the less capable device is automatically selected, and a synchronization message containing the selected data transmission method is formed and delivered as acknowledgment.
To improve the reliability of the detection of the data transmission method from the synchronization message in the receiving device, it is advantageous for a device to send a synchronization message multiple times, the receiving device intepreting the data transmission method as detected when this has been identically determined multiple times.